The present invention relates to a method of powering-up battery powered apparatus which includes means for interrupting the powering-up process should the supply voltage drop below a critical level. Such apparatus includes battery powered radio units, lap-top computers, camcorders and CD players.
When switching-on battery powered apparatus the effect of instantly applying a load to the battery is a sharp drop in the supply voltage. If the apparatus includes supply voltage monitoring means then this sharp drop in the supply voltage may interrupt the switch-on process but as the supply voltage rises the switch-on cycle restarts causing the supply voltage to drop again. This cycle of switching-on, -off and -on again is known in the art as xe2x80x9cmotor boatingxe2x80x9d. In order to avoid motor boating, power supply circuits of the apparatus frequency include a high value capacitor to maintain the supply voltage. Since a high value capacitor is physically large, it is desired to avoid using such a solution when making smaller apparatus in which space is a premium.
An object of the present invention is to power-up reliably battery powered apparatus.
According to a first aspect of the present invention there is provided a method of powering-up a battery powered equipment by a phased activation of a function to increase the current consumption which avoids an excessive transitory drop in the supply voltage from the battery (or supply source).
According to a second aspect of the present invention there is provided a battery powered equipment having means for effecting the phased activation of a function to increase current consumption in a manner which avoids an excessive transitory drop in the supply voltage from the battery (or supply source).
The present invention is based on the realisation that newer batteries, such as lithium-iron high capacity batteries, exhibit a transitory voltage drop when substantial currents are drawn from them. The transitory voltage drop, which may last for less than 10 ms, can be sufficient to cause problems for circuit devices, such as a microcontroller, in which operation outside their specification may lead to loss of values being stored in a memory or even to a reset of the device. By avoiding the production of an excessive transitory drop in the battery supply voltage these problems can be mitigated without requiring a high value capacitor.
The current consumption may be increased in stages by activating circuit stages in succession. The activation of each stage is effected after the battery voltage has recovered, this being done by for example monitoring the battery terminal voltage and switching-on the next following stage once the voltage has recovered or modelling the battery voltage supply curve and estimating the time interval between adding an increment of load and the voltage supply curve recovering and in operation waiting at least the estimated time interval before making another incremental increase in the load.
In the case of needing to power-up reliably a high current consuming load use can be made of at least one dummy load which consumes say about half the current of a real load. In operation, in a first powering-up phase the dummy load is connected to the battery and once the battery has recovered then in a second phase (or subsequent phase if more than one dummy load has to be used) the real load is connected to the battery, whilst the dummy load(s) is (or are) disconnected, enabling a high current to be supplied whilst avoiding the risk of incurring an excessive transitory voltage drop.
Although the time spent drawing partial load currents wastes some energy, an advantage of avoiding significant voltage drops is that the battery can be operated longer as it will decay steadily until it reaches its end point. Thus the total battery lifetime is increased which is of significance in battery powered telemetry apparatus, for example automatic meter reading apparatus, in which the operation of exchanging of batteries has a high relative cost.